The basic purpose of this project is to examine the physiological and biochemical mechanisms uderlying the calcium transport systems of the two major subcellular structures, sarcoplasmic reticulum and sarcolemma, involved in regulating sarcoplasmic calcium levels in bovine aortic smooth muscle. The basic approach will be to prepare fractions from the aortic muscularis, using differential centrifugation and discontinuous sucrose gradients, which are selectively enriched in sarcoplasmic reticulum and sarcolemma. Each fraction, once a preparation scheme has been devised, will be examined for the kinetics of its calcium transport system, the calcium fluxes, both efflux and influx, and the associated ATPase activities. Further experiments will be performed to determine the influence of variations in K ion, Mg2 ion, H ion and ATP levels on the calcium transport properties of the two subcellular fractions. The sarcoplasmic reticulum will also be examined for a phosphorylated intermediate associated with its calcium transport system analogous to such an intermediate found in striated muscle sarcoplasmic reticulum. If such an intermediate is demonstrable, its linkage will be characterized and the temporal relationship between phosphorylated intermediate levels, calcium transport and associated ATPase activity will be determine. These results will be incorporated into a net thermodynamic model describing sarcoplasmic Ca ion levels in vascular smooth muscle.